The invention herein is generally concerned with the feeding of web material to high speed rotary treatment apparatus, particularly die cutting apparatus and the like. More specifically, the invention is concerned with a system for the elimination of web material waste between successive blanks treated or cut from the web. The minimization of this waste has long been a goal, with a particularly efficient system set forth in U.S. Pat. No. 3,756,149, issued on Sept. 4, 1973 to Thomas Bishop.
The Bishop apparatus, through cam controlled feed rolls and uniform acceleration, in both a forward and reverse direction, achieves a pullback of the web material during those periods of disengagement by the treatment means or die. While the web control achieved by Bishop U.S. Pat. No. 3,756,149 is significant and results in a substantial reduction in waste in a structurally simple and efficient manner, the Bishop apparatus does not provide for a complete elimination of waste between impressions of the trailing edge of the die and the subsequently encountered leading edge thereof.
The complete elimination of waste, aside from the obvious economic advantages, becomes particularly significant when producing blanks with an interrupted or two-pass cut. This requires extreme accuracy in aligning the leading edge of a cut with the previously formed trailing edge to produce a blank without distortion or variation in length.
Bishop, U.S. Pat. No. 3,756,149, is not capable of providing the accuracy required for a proper interrupted cut. This is primarily because of the lack of any provision, in Bishop, for the accommodation of the overfeeding of the web occurring in general both during the initial engagement of the die with the web and at the point of disengagement therefrom. Basically, due to the thickness of the web material and the penetration of the die rule into the complementary roll, the leading cutting edge of the die will normally engage the web material and effect a positive forward driving thereof prior to the aligned centers of the rolls. This engagement continues with the trailing edge of the die remaining in driving contact with the web material a distance beyond the centerlines. This in turn results in an excess positive forward feed of the web material by a length equal to the sum of these two distances. Bishop, U.S. Pat. No. 3,756,149, while providing for a deceleration, stopping and reversing of the web after the trailing edge of the die has left the nip, then proceeds to position the trailing end of the blank on the web at the nip or slightly beyond the nip when the leading edge of the die reenters the nip. Thus, there is no recognition of the problem of die engagement prior to the aligned roll centerline and disengagement subsequent thereto. As such, an inherent amount of waste material is retained.
In a further attempt to reduce or eliminate waste between cut or printed blanks, and without an indication of recognition of the inherent problems of pre-engagement and post disengagement of the die with the web, Bishop, in U.S. Pat. Nos. 4,147,078 and 4,153,191, proposes rather elaborate systems, including multiple sets of feed roll pairs and photoelectric sensing and control systems.